How do you measure one rep max?

So, when I began this blog in December it was really the next step in trying to figure out my next step in training.  I was working with Nancy Arnold (aka The Big Girl) on her bodybuilding routine and learning a lot about bodybuilding nutrition and training regimens.

Looking a Jon Yeo's (now defunct) weblog and Scott Bird's Straight to the Bar, I noticed people mentioning  a lot of PRs (personal records).  Nancy and I started to report them to for our multi-rep bodybuilding routines.  Of course, nothing was comparable, and as Scott pointed out, it was hard to keep track.

So, now we're about to launch on this periodization routine, and we've decided to measure one rep max (1RM).  The question is: how do you measure 1RM and what for?  I think we are going to pick some benchmark exercises and do it for those.  Stay tuned.